First, I think proxies have their place. Please don't mistake my comment for any issue with proxies themselves.
Second, the don't need Git part is a bit of misdirection. Other package manager (Composer for PHP comes to mind but there are others, too) can pull the source at a version right for GitHub. This is much faster than using Git and people have been doing it for some time. Typically it's pulled down as a tarball.
You don't need a proxy to have git out of the loop for downloads or install time stuff.
Third, when it came to making tradeoffs one was made here. I don't know if it was explicit or not. Protections from the global checksum database as a default were put ahead of privacy as a default.
I wonder what other designs could have kept a certain amount of the global checksum protection while keeping privacy. I came up with a few idea while considering my response here.
Fourth, to really speed up performance in things like CI it's much faster to cache the modules locally. This is something used across programming languages for dependencies and most of the major CI systems have this documented. I looked at using GoCenter months ago but didn't opt for it because caching in CI was so much faster.
We were looking at things holistically rather than just with a single tool.
As I said in the blog post, I appreciate the privacy policy being up front. It is the first link on the proxy website. And, I appreciate the configuration to customize the proxy.
A lot of this has to do with the default. Most people won't change it. A lot of people are going to leak proprietary information to Google without realizing it. Everyone here can decide if that is a good or bad thing for themselves. Hopefully, they will learn the config to customize things if they want.